The present invention relates to processes of varying an electric current and variable-type inductors having closed loop characteristics, and, more particularly, to horizontal linearity compensation processes and circuits to compensate for broadband horizontal linearity with low electric power by using the electric current variable-type inductor having closed loop characteristics.
In general, a cathode ray tube (CRT) employed for a video display device uses a principle of displaying different brightness and colors as different amounts of electron beams strike fluorescent materials of red, green, and blue (RGB) colors coated on the surface of the cathode ray tube according to a intensity of a video signal, which is widely used because of the low price and the excellent display performance. The video card supports various video modes for each of which different horizontal and vertical frequencies are generated based on a resolution to be displayed. As the horizontal and vertical frequencies are increased from low to high, display flickering is reduced so that the eye fatigue of a user is lessened.
Multi-mode video display devices are referred to as video display devices that are compatible with two or more video modes, with a deflection circuit and various deflection compensation circuits used to adjust diverse horizontal frequencies adjustment of image sizes and positions. The left and right widths from the center of the screen are not symmetrical if a horizontal frequency is varied for a multi mode video display device. In order to compensate the left and right widths to be symmetrical, a horizontal linearity compensation circuit is generally provided in the video display device. The horizontal linearity compensation circuit typically includes a compensation current supply that provides a compensation current that varies in magnitude and direction, and a current variable inductor is connected in series to the horizontal deflection coil in order to compensate the magnitude and direction of a sawtooth current flowing in a horizontal deflection coil, in accordance with the magnitude and direction of the compensation current.
The inductance of the current variable inductor varies in consonance with the horizontal frequency, so that the left and right widths of the screen with respect to the center of the screen are symmetrical. In order for the left and right widths of a screen to be adjusted to be exactly symmetrical, a current variable inductor may be constructed for a conventional horizontal linearity compensation circuit, with a primary coil is wound on the first drum core, a secondary coil is wound on the second drum core, and the first drum core is stacked on the second drum core. Generally, the number of turns of the primary coil is substantially greater than the number of turns in the secondary coil. In order to maintain a proper inductance, the ferrite magnet is mounted on the lower portion of the second drum core. The inductance change of the secondary coil changes according to the amount of magnetic flux generated by the primary coil. The magnetic flux is symmetrically generated in the left and right sides of the primary coil and the secondary coil to form an open loop outside the cores drum. When the degree of mutual coupling between the drum cores and the ferrite magnet deteriorates, a near short-circuit current flows in the primary and secondary coils to compensate horizontal linearity because an open loop type is applied to the current variable inductor using the first and second drum cores, and a ferrite magnet. Accordingly, we have found that a problem occurs because of the large number of turns required in the primary coil to generate a power loss.
Moreover, since the variable range is limited according to the magnitude of the horizontal deflection current, a lot of current in the primary coil flows in order to solve the limitation. Therefore, there exists another problem in that an additional loss of power occurs and then more heat is accordingly generated. We have also noticed that a further problem occurs when the uniformity of display brightness deteriorates because the electron beam in the cathode ray tube is distorted by the magnetic flux generated from the ferrite magnet.
Accordingly, it is an object of the present invention to provide an improved process of varying an electric current and variable-type inductor having closed loop characteristics.
It is another object to provide a process of varying an electric current and a variable-type inductor having closed loop characteristics with an I-shaped core arranged between two E-shaped cores.
It is still another object to provide a current variable inductor that exhibits closed loop characteristics with an I-shaped core arranged between two E-shaped cores.
It is yet another object to provide a horizontal linearity compensation circuit in order to compensate for broadband horizontal linearity with low power by using a current variable coil having the closed loop characteristics.
In order to achieve these and other objects, a current variable inductor having the closed loop characteristics according to the present invention is constructed by arranging a leg of a first E-shaped core and a leg of a second E-shaped core opposite to each other, arranging an I-shaped core between a first E-shaped core and a second E-shaped core, contacting the I-shaped core with the first E-shaped core, spacing the I-shaped core apart from the second E-shaped core, winding a primary coil around a center leg of the first E-shaped core, and winding a secondary coil around a center leg of the second E-shaped core.
Further, in order to achieve these objects, the horizontal linearity compensation circuit according to the present invention comprises a horizontal deflection part for deflecting a scanning electron beam in a horizontal direction by a sawtooth wave flowing in the horizontal deflection coil; a controller outputting a control signal according to a horizontal frequency; a compensation current supply part for outputting a compensation current of which magnitude and direction vary according to the control signal; and an inductor having an I-shaped core arranged between a first E-shaped core and a second E-shaped core and having a primary coil wound around a center leg of the first E-shaped core and a secondary coil wound around a center leg of the second E-shaped core, and for compensating a magnitude and a direction of a sawtooth wave current by varying an inductance thereof according to a magnitude and a direction of the compensation current, wherein a leg of the first E-shaped core and a leg of the second E-shaped core are arranged opposite to each other, the I-shaped core is in contact with the first E-shaped core, the I-shaped core is spaced apart from the second E-shaped core, the compensation current flows in the primary coil, and the sawtooth wave current flows in the secondary coil. In contradistinction to conventional current variable inductors with open loop characteristics, a current variable inductor with the closed loop characteristics of the present invention, may be constructed with the number of turns in the primary and secondary coils greatly reduced so as to reduce the likelihood of a thermal breakdown of the coils, and prevent the electron beam in the cathode ray tube from being distorted by a magnetic flux generated from a ferrite magnet because the ferrite magnet has been eliminated. Moreover, a horizontal linearity compensation circuit constructed according to the principles of the present invention enables optimum display linearity to be attained by compensating a broadband horizontal linearity with a low power by using a current variable inductor having the closed loop characteristics.